For dental drilling of bone tissue, a tool tip or bur on the head of a handpiece is rotated at a high speed. However, when the cutting load increases, rotating speed is reduced significantly. To measure the rotating speed under varying load is desirable for proper treatment, useful for data analysis of clinical experiments, and necessary to control the rotating speed at a constant value. Measurement of speed variation is a requisite to activating any automatic feedback feature for spontaneous modification of the power input to the motor. For these purposes, prior art attempts to detect the rotating speed of the motor for a micro-motor driven handpiece were based upon motor drive voltage or current. However, this attempt has not been successful, since the rotating speed is detected indirectly via voltage or current, and thus large errors are caused.
One attempt to bypass the shortfalls of the described motor drive voltage approach is a magnetic speed detection system as described in Tachibana U.S. Pat. No. 4,493,643 granted Jan. 15, 1985. While this is a non-contact rotating speed detection device, based on an electromagnetic induction pulsed generator, the electronic complexity, the special materials required, and the complex handpiece redesign make this system economically unattractive for general professional dental use.